|Publication number||US6879932 B2|
|Application number||US 10/725,926|
|Publication date||Apr 12, 2005|
|Filing date||Dec 3, 2003|
|Priority date||Dec 13, 2002|
|Also published as||DE60310865D1, DE60310865T2, EP1428442A1, EP1428442B1, US20040162701|
|Publication number||10725926, 725926, US 6879932 B2, US 6879932B2, US-B2-6879932, US6879932 B2, US6879932B2|
|Inventors||Joël Baudou, Alain Leger|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (14), Referenced by (4), Classifications (11), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
1. Field of the Invention
The invention concerns the ergonomics and safety of head equipment, notably incorporating display devices, intended to be worn by aircraft crew.
The use of so-called visionic display devices mounted directly on the user's head rather than on the instrument panel has many advantages. For example, it is possible to compensate the human vision when ambient light conditions become insufficient by means of light-intensifying night-vision devices. It is also possible to complement the user's natural vision by displaying symbols and synthetic images.
However, these devices incorporating image sources, optical components, mechanical parts, etc. have non-negligible weight and substantially increase the total load supported by the spinal column. This additional load is particularly inconvenient in that its center of gravity does not coincide with that of the head. Aircraft crews are, moreover, subject to very strong mechanical stresses (vibrations, accelerations, ejection thrust, parachute opening, crashes, etc.) which further increase the loads to which the spinal column is subjected. Moreover, the upper spinal column is known to be relative vulnerable to strong accelerations, with a risk of severe injury or even death.
The design of head-mounted visionic systems takes into account this type of risk in an effort to reduce it to an acceptable level by applying general rules and recommendations to limit the equipment mass and better position its center of gravity.
Knowledge of the position of the head's center of gravity is therefore important for head equipment designers.
2. Description of the Prior Art
The equipment characteristics are well defined and relatively easy to calculate and measure. CAD (computer-assisted design) tools are able to calculate, on the basis of the design, the provisional weight of the helmet equipment and the position of its center of gravity. On the other hand, it is much more difficult to know precisely the mechanical characteristics of the user's head. So-called “standard” head models are traditionally used. However, these models can lead to false conclusions regarding the anatomic particularities of certain users and incorrect calculation of the head's center of gravity.
The object of the present invention is to overcome the disadvantages of using a “standard” head—whose biomechanical parameters may not correspond to those of the head of a real user—by substituting a representative digital model enabling of a more precise calculation of the exact position of the center of gravity of the head.
More specifically, the object of the invention is a process for determining the position of the center of gravity of head equipment worn by a user relative to the center of gravity of the user's head, said head equipment including display devices, characterized in that said process includes at least the following steps:
The invention will be better understood and its other advantages will become evident on reading the detailed description below of an embodiment, which is non-limitative and taken only as an example, with reference to the attached drawings of which:
Modern 3D anthropometric techniques are already used for personalizing the head equipment of aircraft crews. This approach avoids the need to fit head equipment with mechanical adjustment means to present the image generated by display systems to the wearer's eyes, such systems adding unnecessarily to the complexity and weight of the helmet.
One simple way of implementing the invention is to use these existing techniques to calculate the center of gravity of the user's head, in which case the basic digital model is a three-dimensional mapping of the external surface of the user's head, the anatomical data then being points on this surface.
One of the difficult aspects of this mapping is to define a precise triaxial reference frame in which the form of the head is perfectly defined, in order to be able to calculate the centers of gravity of the head and the equipment in the same reference frame. The simplest approach is to define identifiable anthropometric points, said points enabling the head to be referenced in a second triaxial reference frame (O, X, Y, Z) whose position is defined relative to the first triaxial reference frame of the head equipment. As shown in
The three-dimensional mapping is traditionally performed by optical means such as optical cameras or laser-scanning optical scanners. The anthropometric points mentioned previously are identified simply by colored marks or dots affixed to the user's head. In addition to these devices, a color camera can be used to display the texture of the head surface and point to the various anatomical points of the head.
Once the three-dimensional mapping is completed, the position of the head's center of gravity CGT can be calculated from this mapping. The position of the center of gravity can be calculated from that of the center of volume CVT of the head.
Among the processes used to perform this calculation, it is possible to determine the position of the head's center of volume by applying a first process whose steps are illustrated in
This first process is quite suitable when the points of the three-dimensional mapping are digitized in a standard ASCII-type format, since the calculations determining the head's center of volume are a sequence of simple elementary operations.
It is however possible to use a different process to determine the position of the head's center of volume. The steps of this second process are:
This second process has the advantage of being able to use the head's digital model as a CAD object, which then makes it possible to perform simulations such as the positioning of head equipment on the user's head.
Whatever process is chosen, the sectional plane PC delimiting the head at neck level can be unique. It is then determined substantially by the left gonion 5, the right gonion 5 and the inion 6, as shown in FIG. 3.
The head can also be delimited at neck level by a combination of two sectional planes P′C and P″C, the first sectional plane P′C delimiting the volume of the head to the front, the second sectional plane P″C delimiting its volume to the rear. The first sectional plane is defined substantially by the left and right gonions 5 and the right and left occipital condyles 7; the second sectional plane is defined by the right and left occipital condyles 7 and the inion 6. In this case, the common point M preferentially lies on the intersection of these two sectional planes P′C and P″C, as shown in FIG. 4.
Knowing the position of the center of volume of the user's head, the position of the head's center of gravity can be deduced in the second triaxial reference frame of the head by using the following formula for each of the 3 coordinates XCGT, YCGT and ZCGT of the head's center of gravity:
X CGT =A X ·X CVT +B X ·L+C X ·I+ . . .
Y CGT =A Y ·Y CVT +B Y ·L+C Y ·I+ . . .
Z CGT =A Z ·Z CVT +B Z ·L+C Z ·I+ . . .
More generally, the position of each of the three coordinates of the head's center of gravity in the second triaxial reference frame is obtained by the sum of products of two factors, the first factor being a constant, the second factor being an anthropometric parameter of said head.
It is also possible to determine the head's center of gravity using a digital model that gives not only the three-dimensional mapping of the head, but also the volumetric and densitometric characteristics of its various constituents (skull bone, brain, cavities, etc.). These data are obtained, for example, using NMR (Nuclear Magnetic Resonance) tomographic imaging means.
When the volume, weight and position of the center of gravity of the user's head are known, these data can be input to bio-numerical simulation tools such as, for example, the PAM-SAFE software developed by PAM SYSTEM which can be used to create a digital model representative of each user. By applying stresses representative of real flight conditions on this digital model, the stress tensor at the head-neck interface can be computed. It is then possible to assess the risk for each user of wearing head equipment, taking account of injury criteria associated with acceptable stresses.
The result of this analysis can be exploited in several ways, for instance to:
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|Citing Patent||Filing date||Publication date||Applicant||Title|
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|U.S. Classification||702/150, 2/6.1|
|International Classification||G02B27/01, G02B27/00, A42C2/00|
|Cooperative Classification||G02B2027/014, A42C2/007, G02B2027/0138, G02B27/017|
|European Classification||G02B27/01C, A42C2/00D|
|Apr 30, 2004||AS||Assignment|
Owner name: THALES, FRANCE
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:BAUDOU, JOEL;LEGER, ALAIN;REEL/FRAME:015287/0560
Effective date: 20040109
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